https://leetcode.com/problems/sqrtx/

sqrt_binary.java

//https://leetcode.com/problems/sqrtx/
public int mySqrt(int y) {
        //return (int)Math.sqrt(x);
        long L = 0, R = (long)y + 1;//[0,y)
        long ans = 0;
        while(L < R){
            long mid = (L + R) / 2;// guess mid
            if(guess(mid, y)){
                ans = mid;
                L = mid + 1;
            } else {
                R = mid;
            }
        }
        return (int)ans;
    }
    
    public boolean guess(long x,long y){
        return x * x <= y;
    }